Barriers to high school and university students’ physical activity: A systematic review

Physical inactivity commonly occurs throughout one’s life, particularly during adolescence and young adulthood. Multiple factors can negatively influence participation in physical activity, but there has been no review examining the barriers to physical activity among high school and university students. Therefore, the aim of this systematic review was to summarize evidence of barriers to the practice of physical activity among high school and university students. The literature search was conducted without time limits using five databases, including CINAHL, Cochrane Library, Embase, PubMed, and Scopus. In total, 59 studies (37 with high school students [n = 22,908] and 22 with university students [n = 15,411]) were included. The main barriers identified in high school and university students were lack of time, lack of motivation, and lack of accessible places. These findings may be useful in designing and implementing evidence-informed interventions and programs for physical activity promotion in students.


Introduction
Chronic non-communicable diseases (e.g., cancer, diabetes, respiratory, and cardiovascular diseases) are a major current public health issue and responsible for more than 70% of worldwide mortality in adults [1,2]. In adults, these diseases result in days of lost work and reduced productivity, in addition to affecting quality of life [3]. In children and adolescents, these diseases affect several domains (e.g., social, emotional, cognitive, physical) of wellness, which in turn creates the risk of decline in academic performance and school attendance [4]. Therefore, regular physical activity has been considered a significant factor in the prevention of chronic non-communicable diseases [5][6][7]. Recent studies have identified physical and psychological benefits associated with regular participation in physical activity. For example, physical benefits resulting from physical activity include body weight regulation [8,9], blood pressure reduction [10], better bone health [11], and improved muscle strength and function [12]. a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 activity among high school, college, and university students. The current systematic review includes different types of studies and covers a broad population group (ranging from high school students who are in their late adolescence to undergraduate students who have just transitioned into young adulthood) and study designs (both qualitative and quantitative). The information obtained from this review can provide a better understanding of the barriers encountered by students in meeting the recommended levels of physical activity, which may be helpful for designing and implementing evidence-informed interventions and programs for physical activity promotion as well as for informing environmental modifications to improve students' physical activity.

Protocol and registration
This systematic review follows the PRISMA guidelines [62] for identification, screening, eligibility, and inclusion of primary studies. The protocol for this review was recently published [58], and it was registered in the PROSPERO (CRD42020198899). Ethical approval was not required because this study does not involve any human participants.

Identification and selection of studies
The literature search was performed on November 5, 2021, using the following five bibliographic databases: CINAHL, Cochrane Library, Embase, PubMed, and Scopus. The search terms for the key concepts-"students," "high school/university," "barriers," and "physical activity"-were combined using Boolean operators (AND/OR), with no restriction on publication year. The search strategy was adapted for each database. The detailed search strategy is described in S1 Table. Secondary searches were performed by manually searching the reference lists of articles included in this review (reference lists of studies eligible for inclusion were searched to find potentially eligible studies).
The eligibility criteria were specified according to the Population, Exposure, Outcomes, and Study (PEOS) framework for the research question [63-65]: "P" referred to high school and/or university students, comprising adolescents or adults of both sexes aged between 10-30 years; "E" corresponded to barriers to physical activity; "O" constituted the practice of physical activity; and "S" referred to studies with qualitative and quantitative designs published during any year in peer-reviewed journals in English, Spanish, or Portuguese.
For this review, studies that targeted students in the aforementioned age group were eligible for inclusion. The World Health Organization defines "adolescents" as individuals aged 10-19 years and "youth" as individuals aged 15-24 years; thus, "young people" are individuals who range in age from 10 to 24 years [25]. The extension of the age range to 30 years was justified by the fact that this age range would also cover university students who are enrolled in undergraduate courses [66][67][68]. Therefore, the age up to 30 years was meant to cover undergraduate university students.
Physical activity is defined as "any bodily movement produced by skeletal muscles that requires energy expenditure" [69]. Physical activity broadly includes walking, cycling, swimming, playing sports, and performing recreational activities [7]. Barriers refer to factors that prevent or hinder an individual's participation in physical activity [46]. Systematic or narrative reviews; case studies; opinion articles; letters; replies; conference abstracts; theses or dissertations; book chapters; and studies that included people with physical and/or mental disabilities, groups with chronic diseases, and pregnant or lactating women were excluded. In addition, studies on specific and/or traditional communities (e.g., rural, indigenous, refugees, isolated, and aboriginal) and studies with mixed age samples were excluded.
The results of the database searches were imported into the Mendeley software, where duplicate studies were identified and excluded. Two reviewers (RMFS and CRM), who were trained to screen articles, independently evaluated the titles and abstracts of the studies according to the eligibility criteria. After this stage, studies available online was assessed to determine their inclusion. Any disagreements were resolved by involving a third reviewer (MN). All the steps involving study screening were performed in the Rayyan [70] software.

Data extraction
The following data were extracted from the included studies: author and year of publication, type of study, country, population, sex, age group, data collection instrument, and barriers to physical activity. We categorized the results into two groups: (a) high school students and (b) university students. The information was extracted independently by two reviewers (RMFS and CRM), and disagreements were resolved by a third reviewer (MN).
The factors included in the socioeconomic and demographic category were: age, sex, socioeconomic status, anthropometric characteristics, and ethnicity. The psychological, emotional, and cognitive category included: motivation for or interest in physical activity, benefits of physical activity, desire to exercise, mood disorders, perception of health and physical competence, lack of time, lack of desire, and laziness. The factors in the sociocultural category constituted: social support from family, friends/peers, and teachers or significant others. The environmental category included: access to equipment, climate, and program costs. The

PLOS ONE
factors in the physical activity characteristics category were: intensity and subjective feeling of physical effort. Finally, the behavioral attributes category included: history of previous activity and process of change [71].

Methodological quality and risk of bias
The quality of the evidence from cross-sectional and longitudinal studies was evaluated using the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) [72]. In accordance with the GRADE ProGDT online software, evidence was classified into high quality, moderate quality, low quality, and very low quality [73].
The risk of bias in quantitative studies was analyzed using the 27-item Downs and Black checklist [74]. As some items of this checklist were not applicable to observational study designs, a shorter version, adapted from a previous study, was used for cross-sectional (0-12 points) and longitudinal (0-16 points) designs [75]. Therefore, a subset of 16 questions (corresponding to Questions 1-3, 5-7, 9-12, 17, 18, 20, 21, 25, 26) was used. The score for each study was calculated as a percentage of the total score, and scores above 70% were considered "low risk of bias," while scores below 70% were considered "high risk of bias" [74].
The quality of evidence and the risk of bias in qualitative studies was classified using the 10-item Critical Appraisal Skills Program (CASP) qualitative research checklist [76]. The overall scores were classified as low quality (one star; 0-3 points), medium quality (two stars; 4-7 points), and high quality (three stars; 8-10 points) [77].
For all studies, information on the declaration of potential conflict of interests and ethical approval was extracted. The analysis of the quality of the evidence and bias risk was performed independently by two trained reviewers (RMFS and CRM), and disagreements were resolved by a third reviewer (MN). The reviewers were trained in the use of instruments to analyze quality of evidence and bias risk before beginning their assessment [78].

Description of the selected studies
A total of 6,384 records were imported after searching literature in five databases. Of these, 2,586 duplicates were removed, and 3,658 were excluded based on title and abstract screening, leaving 140 studies for full-text assessment. Eighty-one irrelevant studies were excluded, leaving 59 studies for inclusion in the review (37 on high school students and 22 on university students) (Fig 1). No studies were found through secondary (i.e., reference) searching.
The questionnaires examining barriers to physical activity in high school students were the Barriers to Physical Activity Questionnaire (n = 4, 10.8%) [129,131,134,135] and Perceived Barriers to Physical Activity Questionnaire (n = 2, 5.4%) [79,116]. The questionnaires examining barriers to physical activity in university students were the Exercise Benefits/Barriers Scale (n = 5, 22.7%) [89,92,94,120,121], A List of Possible Barriers to Physical Activity (n = 2, 9.0%) [127,128] and Barriers to Being Active (n = 2, 9.0%) [118,136,137]. The detailed characteristics of the studies on high school and university students are shown in Tables 1-3. For both high school and university students, the most frequently perceived barriers to physical activity were in the 1) psychological, emotional, and cognitive; 2) environmental; and 3) sociocultural categories. In particular, the psychological, emotional, and cognitive barriers were the most frequently reported in both quantitative and qualitative studies. In studies on high school students, 32 (86.4%) barriers belonged to the psychological, emotional, and cognitive category, whereas for university students, 18 (81.8%) corresponded to this category. Table 4 presents the main barriers (factors) for each category according to study design.

Quality of studies and risk of bias
Thirty-four (91.8%) studies on high school students and 19 (86.3%) on university students had explicitly stated that they sought ethical approval. Conflicts of interest were declared in 10 (27.0%) studies on high school students and 10 (45.4%) on university students. The quality of the evidence for 16 (66.6%) studies on high school students and 15 (88.2%) on university students, using the cross-sectional and/or longitudinal design, was classified as "low quality." Sixteen qualitative studies had high methodological quality. Most studies on high school students

PLOS ONE
had a low risk of bias (i.e., they had scores above 70%), whereas most studies on university students had a high risk of bias (i.e., they had scores below 70%). The description for the quality of studies and risk of bias is presented in Tables 5 and 6.

Discussion
This systematic review summarizes the findings of qualitative and quantitative research on barriers to physical activity and their dimensions in high school and university students. A total of 38,319 adolescents and young adults from 31 countries were part of the studies included in our review. The main barriers identified in high school and university students were lack of time, lack of motivation, and lack of accessible places.
The findings of the current review suggest that psychological, emotional, and cognitive factors were the most examined in quantitative studies (92.0% of studies with high school students and 94.0% with university students), whereas environmental (83.3% of studies with high school students) and sociocultural (75.0% of studies with university students) factors were most frequently studied in qualitative studies. Furthermore, the main barriers to physical activity in high school students were related to the following dimensions: psychological, emotional, and cognitive (lack of time and motivation); sociocultural (lack of social support); and Internal factors (e.g., lack of ability and lack of enjoyment), Existing stereotypes (e.g., boys will always be better in sport, family context, media), Other hobbies (e.g., lack of time, prefers cooking and other artistic activities) and Teachers (e.g., lack of attention the teachers, always praise the best students).

PLOS ONE
environmental (lack of accessible places). Previous studies have also identified these barriers and dimensions as the most common [139][140][141]. In addition, a recent systematic review identified these dimensions as the most common in terms of barriers to physical activity in adolescents [57]. For the environmental dimension, a previous study suggested that schools must work with community partners and officials to provide environments that optimally support physical activity in adolescent students [142].
The main barriers to physical activity in undergraduate university students were related to the following dimensions: psychological, emotional, and cognitive (lack of time and

PLOS ONE
motivation); environmental (lack of accessible places); and socioeconomic and demographic (lack of financial resources). Barriers in the psychological, emotional, and cognitive category were identified in almost all parts of the world that were covered by the included studies. Among others, lack of time was the most cited barrier to physical activity in university students. Although no previous systematic reviews have identified barriers to physical activity among university students, some qualitative studies have shown the presence of motivational and time-related barriers as factors preventing university students from practicing physical activity [122,143,144]. Furthermore, barriers to physical activity are almost similar in reviews on different populations, for example in individuals from the Middle East and North Africa [145], pregnant women [146] and medical services professionals [147]. A recent systematic review showed that cultural values (e.g., general and gender norms) affect the practice of physical activity in specific countries (e.g., Arab countries) [148]. Further, it is important to note that access to university is restricted by socioeconomic status: adolescents and young adults with a lower socioeconomic level have less access to higher education, which may also be related to a greater social and cultural barrier to physical activity. Furthermore, socioeconomic barriers permeate all other barriers. For example, motivation for physical activity, knowledge of its benefits, time availability, social support from family, and access to equipment are negatively influenced by socioeconomic vulnerability [149]. Many behavior change theories [150][151][152][153][154][155], health behavior adoption theories [156,157], and social ecological models [158,159] have been used to promote active lifestyles in different population groups. However, behavior change is a complex and multifaceted phenomenon with multiple levels of influence [152]. Therefore, multilevel physical activity interventions targeting several components (e.g., individuals, social and physical environments, and policies) have been shown to have promising effects [160][161][162][163]. Intrinsic motivation is an important factor used to determine active participation in physical activity and sport [35]; thus, to increase adolescents' daily physical activity, special focus should be paid on increasing their intrinsic motivation [168]. Some studies have also pointed out the importance of context in PLOS ONE Table 5. Methodological quality and strength of evidence for studies examining barriers to physical activity in high school students.

Qualitative study (n = 12) Conflict of interests Ethical approval CASP
Screen time was not identified as a barrier to physical activity, but it may be related to the "lack of time" barrier since spending more time on a device means having less time for other activities, including physical activity. A study with Spanish teenagers found that those who spent more time in front of screens spent less time performing physical activity [171]. In addition, screen time was reported as the main driver for adolescents' inability to meet the recommendation of moderate-to-vigorous physical activity in the United Kingdom [172]. Understanding the barriers to physical activity is important because it may provide information useful for creating public health and educational policies. Thus, actions and programs to Table 6. Methodological quality and strength of evidence for studies examining barriers to physical activity in undergraduate university students.

PLOS ONE
promote the practice of physical activity should always consider all dimensions of physical activity barriers, and special attention should be given to psychological, emotional, and cognitive factors. The current study, as far as we know, is the first systematic review that summarizes the evidence (qualitative and quantitative) for barriers to physical activity practice in high school and university students. However, some limitations should be acknowledged. First, the heterogeneity across included studies did not allow a meta-analysis to be performed. Second, the majority of evidence on barriers to physical activity in high school and university students came from cross-sectional studies (69.49%), with two longitudinal studies. Third, there was a lack of standardization of instruments for identifying barriers to physical activity in students. Finally, gray literature was not included in the review. Therefore, future studies should be conducted with strong methodological rigor to generate better evidence, for example by using longitudinal designs, control bias, and a context-sensitive basis. The use of standardized global instruments for physical activity and barriers, mainly for university students, has also been advocated in a recent review [40].

Conclusion
The barriers to physical activity among high school and university students are mainly related to psychological, emotional, cognitive, environmental, and sociocultural factors. These findings suggest that future behavioral change interventions or interventions targeting barriers to physical activity should prioritize these dimensions. In addition, studies on the least explored dimensions (i.e., physical activity characteristics and behavioral attributes) are needed in the future.